Crystal Space
3D engine, game SDK
Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. It supports: true six degrees of freedom, colored lighting, mipmapping, portals, mirrors, alpha transparency, reflective surfaces, 3D sprites (frame based or with skeletal animation), procedural textures, particle systems, halos, volumetric fog, scripting (using Python or other languages), 16-bit and 32-bit display depth, OpenGL and software renderer, hierarchical transformations, fonts, …
http://crystal.sourceforge.net